Question

What are the major drugs used in treating Parkinson's Disease patients as well as their mechanism of action and side effects?

Answer 1

Parkinson's disease is a neurodegenerative disorder in which the DOPAMINERGIC NIGRO STRIATAL PATHWAY is effected.

I will explain the pathogenesis so,you can easily understand the mechanism of the drugs.

In parkinsonism we will see the loss of co- ordination and movement . Some neurons which are responsible for movement are located in the striatum and this striatum recieves information from

• NEO CORTEX which relays sensory information and plans future action
• SUBSTANTIA NIGRA sends dopamine to co ordinate the inputs.

Physiologically, this dopamine exerts inhibitory effect on GABA ergic neurons in striatum.But now the inhibitory effect on those GABAergic neurons become low . So, the gaba ergic function is increased causing INHIBITION OF THALAMUS AND REDUCED EXCITATORY INPUT TO MOTOR CORTEX.

There is a balance between dopamine and Acetyl choline, now due to decreased dopaminergic activity there is an imbalance causing increased cholinergic activity and leads to manifestations like RESTING TREMOR, RIGIDITY, INSTABILITY, SLOW MOTOR MOVEMENT.

SO, MAIN TREATMENT GOALS OF PARKINSONISM ARE REPLENISHING DOPAMINE OR INHIBITING THE EXCESSIVE CHOLINERGIC ACTIVITY .

• Dopamine is produced within the dopaminergic neurons from the amino acid TYROSINE .
• This dopamine binds to dopaminergic receptors present on the post synaptic neuron
• Excess dopamine is reuptaken back by the pre synaptic neuron
• Dopamine present there is metabolized by enzymes MAO -B and Central COMT.

​​​​​​​Now, we will see some important drugs used in treating parkinsonism .

1) LEVODOPA + CARBIDOPA.

LEVODOPA is a precursor to dopamine. As dopamine cannot cross the blood brain barrier we'll give the dopamine precursor levodopa

Along with levodopa we will give CARBIDOPA to prevent the peripheral metabolism of levodopa. Many peripheral enzymes like DDC(dopamine decarboxylase) a peripheral COMT act on levodopa and CARBIDOPA inhibits DDC .

we can also give ENTACAPONE which inhibits peripheral COMT and inhibits metabolism of levodopa. ENTACAPONE cannot cross blood brain barrier effectively.

SO, BY GIVING THIS DRUG WE CAN INCREASE THE LEVELS OF DOPAMINE IN BRAIN.

ADVERSE EFFECTS :

• Nausea
• Loss of appetite
• Hypotension
• Mental disturbances
• Discoloration of sweat,urine,saliva etc.!

​​​​​​​I'll answer regarding remaining drugs in the comments, sorry for the inconvinience.

I'll post them now it self in comments. :(